1. Field of Invention
This invention relates in general to electronic decoding systems, and specifically to a method for conversion of digitally encoded delta modulated signals to analog form.
2. Prior Art
The goal of a common broadcast system is to take an audio or video signal from a broadcast center, (e.g. voices, music, and/or pictures) and distribute it via a transmission medium (e.g. air, coaxial cable) to a large number of people possessing receivers that can reconstruct the original signal. Consistently high performance can be achieved by encoding the signal digitally before transmission. Digital encoder-decoder schemes, such as linear Pulse Code Modulation (PCM) systems, have good performance for audio applications when the sample rate is greater than about 32 kHz, and each sample is represented by digital words of at least 14 bits. In a linear PCM representation, the quantization levels of the sampled signal are uniformly spaced, so each 14-bit sample represents one of 2.sup.14 equally spaced levels which is closest to the sampled value of the analog signal. The sample rate times the number of bits per sample, or the equivalent bit-rate for good quality audio which is PCM encoded is quite high for broadcast applications however, and PCM signals are not very tolerant of errors that might occur during transmission. Error correction can be employed, but this raises the bit-rate even further. Until several years ago, the implementation of PCM decoders required high precision components, making the decoders very expensive for consumer applications.